1. Field of the Invention
The present invention relates to a molding device, and specifically to a blow molding device for manufacturing a hollow product such as a container of multiple layers.
2. Description of the Prior Art
Conventionally, there has been known a method for manufacturing a multiple layer hollow product wherein a multiple layer parison formed of different kinds of molding material is extruded toward a cavity of a molding die, the material thereafter being subjected to a blowing process to form the hollow product.
Japanese Patent Publication No. 55-39448, published for opposition in 1980, discloses a method for manufacturing a multiple layer hollow container wherein a molding device is provided with a supply screw for supplying a main material, a supply screw for supplying an adhesive, and a supply screw for supplying a barrier resin so that the materials are extruded into a cavity through respective passages to form a multiple layer parison of an inner layer of the main material, an intermediate layer of the adhesive, and an outer layer of the barrier resin. The three-layer parison is then subjected to a blow molding process in which the parison is brought into tight contact with an inner surface of the cavity and cooled down so that a three-layer structure hollow container including three different kinds of materials can be obtained.
U.S. Pat. Nos 4,578,025, 4,565,515, 4,522,775, 4,297,092, 3,321,803, 4,120,633, 4,422,838, 4,302,170, 4,185,954, 4,512,943, and 4,472,129 disclose conventional molding devices. Japanese Patent Publication No. 52-37026, and Japanese Patent Public Disclosure No. 58-220738 also disclose conventional molding devices.
There has been also known a device for manufacturing a five-layer hollow container formed with an outer layer of a main resin material, an inner layer of the main resin material, an intermediate layer of an auxiliary resin material, one adhesive layer between the outer layer and the intermediate layer, and the other adhesive layer between the inner layer and the intermediate layer. The device is provided with a main material extruder for extruding the main resin material, an auxiliary material extruder for extruding the auxiliary resin material, an adhesive extruder for extruding the adhesives, a supply cylinder for receiving the materials from the respective extruders and supplying the materials to a cavity of a molding die, three passages for connecting the respective extruder and the cylinder, and accumulators provided on the respective passages for controlling a supply of the materials.
The cylinder is provided with an annular resin reserving chamber at the lower portion thereof in which a ring member is arranged coaxially with the reserving chamber. The main material from the main extruder is divided by the ring member into the outer layer and the inner layer. The ring member is formed with three annular nozzles or an outer nozzle an intermediate nozzle and an intermediate inner nozzle, which are coaxially arranged with respect to each other. The intermediate nozzle is employed for supplying the auxiliary resin material, and the outer and inner nozzle are employed for supplying the adhesives. Thus, a five layer parison of three kinds of materials is introduced into the cavity.
In the above conventional molding device, the accumulators are provided on the respective passage connecting the extruders and the cylinders corresponding to each of the extruders. It will be therefore understood that it is difficult to control a supply of the materials so as to get a uniform thickness of each of the layers forming the parison.